Technical Field
The present invention generally relates to charge pump circuits. Charge pump circuits are voltage converters that are used in electronic devices such as mobile phones, mobile computers, personal data computers, audio devices and the like.
Charge pump circuits are used in power management circuit in order to replace switched-mode power supply (SMPS) such as boost converters or other DC/DC converters which are expensive due to the cost of an external coil. Thus the same functionality can be achieved with a charge pump circuit which uses only external capacitors.
Related Art
Charge pump circuits provide a regulated output voltage from a different input voltage. For instance the charge pump circuit can be arranged to provide a continuous voltage of +5V from an input voltage varying between 3.9V and 2.3V over time. Typical use is when the input voltage is provided by the battery of a mobile device. As the battery gets discharged, the voltage outputted by the battery diminishes. A charge pump circuit which can generate a 5V voltage from a 2.3V input voltage is, for instance a 3× charge pump circuit that outputs can achieve 3 times the input voltage. Such a charge pump circuit may comprise a tank capacitor positioned at the output of the charge pump which allows outputting a roughly continuous 5V voltage, averaging the charging output voltage and the discharging output voltage.
For some 3× charge pump circuit, the current is consumed at all times by the charge pump while it outputs current only one third of the time. Therefore, almost two thirds of the current is wasted by the charge pump circuit's inherent consumption. The inherent consumption of the charge pump circuit is roughly related to the multiplication factor between the input voltage and a maximum output voltage. Adaptable charge pump circuits are adapted to operate according to different multiplication factors.
Some charges pumps used in mobile application are adapted to operate with any of three modes: 1×5, 2× and 3×, in which, respectively, the charge pump circuit outputs, in a discharging mode, an output voltage worth one and a half times the input voltage, two times the input voltage and three times the input voltage. Therefore, when the input voltage is high, the charge pump circuit is adapted to operate with an efficient 1×5 mode that uses only 1.5 times the current outputted. Conversely, the charge pump circuit is adapted to work in the highly non-efficient 3× mode only when the input voltage is so low that no other solution is available.
Such charge pump circuits may still be improved to be more efficient, especially with higher multiplication factors. There is therefore a need to provide more efficient charge pump circuits.